In vehicles, a manually or automatically operated transmission is provided for varying the power of an internal combustion engine to a required level in accordance with running conditions before the power is taken off from the transmission. This type of transmissions may be classed as a gear type transmission, a belt type transmission and the like, among which the gear type transmission prevails because of a reduced loss of power transmission.
The gear type of manually operated transmission includes a speed change gear train having multiple stages. The gear train is shifted using a shift lever so as to provide gear engagement at different stages. The power of the internal combustion engine is thereby varied to a required point in accordance with running conditions. Then, the varied power is taken off from the transmission.
The aforesaid gear type of manually operated transmission may be classified as, for example, a selective sliding gear type, a constant mesh type, and the like, depending on how a speed change ratio is varied.
The selective sliding gear type of manually operated transmission has respective gears mounted on a main shaft, a counter shaft, and a reverse idler shaft. The main shaft is an input shaft which is connected to and disconnected from the internal combustion engine by means of a clutch that is located on the internal combustion engine side. The counter shaft and the reverse idler shaft extend substantially parallel to the main shaft. In order to transmit the power from the internal combustion engine, a reverse idler gear, which is mounted on the reverse idler shaft, is slidingly brought into engagement with a reverse main gear and a sleeve gear which are positioned respectively on the main shaft and the counter shaft. In addition, the transmission is constructed to allow the reverse idler gear to be operational, even when the vehicle remains stationary.
In the constant mesh type of manually operated transmission, pairs of gears corresponding in number to necessary speed change stages are constantly engaged with each other. Further, the transmission is configured to allow for an idle operation between shafts and the gears. In order to transmit torque, the pairs of gears providing required speed change ratios are fixed to the shafts by means of coupling sleeves that are mounted on the shafts.
In the selective sliding gear type of manually operated transmission, the reverse gears are usually operated while the vehicle is stationary. Accordingly, the transmission provides selective sliding engagement of the reverse gears. However, the sleeve gear of the counter shaft, which is at rest, and the main reverse gear of the main shaft, which continues rotating as a result of inertia after the clutch (not shown) is released, are engaged with one another via the reverse idler gear which is slid on the reverse idler shaft. This causes drawbacks of: the occurrence of gear squeal and a concomitant feeling of uncomfortableness; and, possible damage to portions of the gears and a consequential reduction in gear life.
In order to correct the aforesaid shortcomings, it is only necessary to provide the above reverse gears with synchronizing mechanisms as a constant mesh system in a manner similar to the other gears. However, this is disadvantageous from practical and economical viewpoints because of increased weight, a complicated structure, and high cost.
For this reason, a simpler synchronizing mechanism has been used for only stopping the main shaft from rotating before the reverse idler gear is brought into engagement with the sleeve gear.
As one example of such a construction, there is a known system in which one of the forward stage-synchronizing mechanisms, that is, a second speed-synchronizing mechanism, for example, is lightly actuated at the time of, for example, a reverse-shifting operation which is the time when the speed is changed to a reverse stage. The main shaft is thereby stopped from rotating.
In this instance, the second speed-synchronizing mechanism must be actuated temporarily, and must be released before engagement of second speed gears occurs. To this end, a method in common use is that the second speed-synchronizing mechanism is actuated using the resilient force of a spring, and is released by the spring being driven into contact with a stopper for compressing the spring before the gears are engaged with each other.
A conventional transmission will now be described with reference to the drawings. More specifically, FIGS. 22 through 24 illustrate a transmission of a reverse selective sliding gear type in which a reverse gear squeal-preventing mechanism is not provided. In FIG. 22, 202 denotes a detent-type selective sliding gear type of manually operated transmission (hereinafter simply referred to as a transmission). In addition, 204, 206, 208 and 210 respectively denote a gear section, a differential section, a speed change control section, and a transmission case. The transmission case 210 houses the following shafts: a main shaft 212, which is an input shaft for receiving driving power from an internal combustion engine (not shown) connected and disconnected via a clutch (not shown); a counter shaft 214; and a reverse idler shaft 216. These shafts are disposed in a longitudinal direction of the transmission 202, while extending substantially parallel to each other.
The main shaft 212 is rotatably supported by first and second main shaft bearings 222 and 228. The first main shaft bearing 222 is held at a right wall portion 220 of a right case 218 of the transmission case 210. The second main shaft bearing 228 is held at a left wall portion 226 of a left case 224 of the transmission case 210.
The counter shaft 214 is rotatably supported by first and second counter shaft bearings 230 and 232. The first counter shaft bearing 230 is held at the aforesaid right wall portion 220, while the second counter shaft bearing 232 is held at the aforesaid left wall portion 226.
The reverse idler shaft 216 is rotatably supported by the right and left wall portions 220 and 226.
The main shaft 212 has the following gears fixedly mounted thereon in turn from the internal combustion engine side: a first speed main gear 234; a reverse main gear 236; and a second speed main gear 238. Further, the following gears are rotatably positioned in series on the main shaft 212: a third speed main gear 240; a fourth speed main gear 242; and a fifth speed main gear 244 which is located within a side case (not shown) of the transmission case 210.
In addition, the counter shaft 214 is provided with the following gears in turn from the internal combustion engine side: a final-driving gear 248, which forms a final speed reduction mechanism 246; a first speed counter gear 250, which is engaged with the first speed main gear 234; and a second speed counter gear 252, which is engaged with the second speed main gear 238. The final-driving gear 248 is fixed to the counter shaft 214. The first and second speed counter gears 250 and 252 are rotatably mounted on the counter shaft 214. In addition, the following gears are fixedly mounted in sequence on the counter shaft 214: a third speed counter gear 254, which is engaged with the third speed main gear 240; a fourth speed counter gear 256, which is engaged with the fourth speed main gear 242; and a fifth speed counter gear 258, which is engaged with the fifth speed main gear 244 within the side case.
The reverse idler shaft 216 is fitted with a reverse sleeve 260 and a reverse idler gear 262. The reverse idler gear 262 can be engaged with the reverse main gear 236.
The final-driving gear 248 is held in engagement with a final-driven gear 264 which is provided at the differential section 206.
The counter shaft 214 is fitted with a first and second speed sleeve 266 and a sleeve gear 268 between the first speed counter gear 250 and the second speed counter gear 252. The first and second speed sleeve 266 is positioned on the side of the first speed counter gear 250. The sleeve gear 268, which is integral with the first and second speed sleeve 266, is located on the side of the second counter gear 252. The sleeve gear 268 can be engaged with the reverse idler gear 262.
The counter shaft 214 is further provided with a first speed-synchronizing mechanism 270 between the first and second speed sleeve 266 and the first speed counter gear 250. In addition, a second speed-synchronizing mechanism 272 is positioned on the counter shaft 214 between the sleeve gear 268 and the second speed counter gear 252.
The main shaft 212 is fitted with a third and fourth speed sleeve 274 between the third speed main gear 240 and the fourth speed main gear 242.
A third speed-synchronizing mechanism 276 is disposed on the main shaft 212 between the third and fourth speed sleeve 274 and the third speed main gear 240. Further, a fourth speed-synchronizing mechanism 278 is positioned on the main shaft 212 between the third and fourth speed sleeve 274 and the fourth speed main gear 242.
A fifth speed sleeve 280 is positioned on the main shaft 212 adjacent to the fifth speed main gear 244. Further, a fifth speed-synchronizing mechanism 282 is mounted on the main shaft 212 between the fifth speed sleeve 280 and the fifth speed main gear 244.
The speed change control section 208 is provided with a shifting and selecting shaft 284 which is held to the transmission case 210. The shifting and selecting shaft 284 is differently operated via a control shaft (not shown), depending on a controlled state of a shift lever (not shown). That is, the shaft 284 is axially moved at the time of selecting, while being pivoted about an axis of the shaft 284 at the time of shifting.
The shifting and selecting shaft 284 is provided with an interlocking plate 286 for preventing malfunction. A back portion of the interlocking plate 286 is retained by means of a plate-holding bolt 288 in such a manner that the interlocking plate 286 is slidingly movable only in an axial direction of the shifting and selecting shaft 284. The plate-holding bolt 288 is anchored to the transmission case 210.
The interlocking plate 286 is engaged with a first and second speed-shifting yoke 290. The first and second speed-shifting yoke 290 is mounted on a first and second speed-shifting shaft 292. The first and second speed-shifting shaft 292 is provided with a first and second speed fork 294 which is engaged with the previously mentioned first and second speed sleeve 266.
The shifting and selecting shaft 284 is further provided with a gear-shifting arm 296. A distal end portion of the gear-shifting arm 296 is engaged with a reverse-shifting yoke 298. The reverse-shifting yoke 298 is positioned on a fifth speed and reverse-shifting shaft 300. The fifth speed and reverse-shifting shaft 300 is provided with a lever-holding portion 302, at which an intermediate portion of a reverse-shifting lever 304 is retained.
A root end portion of the reverse-shifting lever 304 is pivotably supported by a lever fulcrum portion 306. The lever fulcrum portion 306 is provided on a mounting bracket 308. The mounting bracket 308 is fixedly attached to the transmission case 210. A distal end portion of the reverse-shifting lever 304 is engaged with the aforesaid reverse sleeve 260. In FIG. 22, 310 denotes a detent-type positioning mechanism.
As illustrated in FIG. 22, in the transmission, the reverse idler gear 262 is freely rotatable during a neutral mode. Further, the main shaft 212 continues to rotate under the influence of inertia after the clutch (not shown) is disengaged. However, since the vehicle is stationary, no rotation is imparted to the counter shaft 214 and the final-driving gear 248, both of which are connected to an unillustrated vehicle shaft.
When a reverse-shifting operation is started, an operating force from the shift lever is transmitted to the reverse gear-shifting arm 296 via the reverse-shifting yoke 298. Then, the reverse gear-shifting lever 304 moves the reverse idler gear 262 in the left direction of FIG. 22 and FIG. 23. As shown in FIG. 23, the reverse idler gear 262 is thereby advanced into engagement with the reverse main gear 236. Since the main shaft 212 is still running at this stage, the reverse idler gear 262 is also turned therewith. However, since the reverse idler gear 262 is in a free state, no gear squeal occurs at the time of gear engagement.
However, as shown in FIG. 24, when the reverse gear-shifting arm 296 further continues to push the reverse idler gear 262, the reverse idler gear 262 is brought into contact with the sleeve gear 268 of the counter shaft 214. At this time, the counter shaft 214 is connected to the vehicle shaft (not shown) via the final-driving gear 248. Therefore, the counter shaft 214 is impossible to rotate. As a result, gear squeal may result from contact between the running reverse idler gear 262 and the sleeve gear 268.
In order to prevent the occurrence of gear squeal, methods have been devised for temporarily ceasing the rotation of the main shaft 212 as shown in FIG. 25.
As one of the methods, for example, a mechanism for stopping the rotating main shaft 212, as illustrated in FIG. 25, has been in practical use. That is, the second speed-synchronizing mechanism 272 is actuated by means of a cam mechanism 352 upon the reverse-shifting operation. The rotating main shaft 212 is stopped by a synchronous action that occurs between the second speed counter gear 252, which is rotated on the stationary counter shaft 214, and the counter shaft 214.
In this instance, if the second speed-synchronizing mechanism 272 is excessively operated under the influence of a shifting action at the time of the reverse-shifting operation, the second speed counter gear 252 is thrown into unexpected operation.
In order to avoid such a phenomenon, the second speed-synchronizing mechanism 272 must be released when being actuated to a certain extent.
In addition, it is desirable that the reverse idler gear 262 is freely rotatable the moment the sleeve gear 268 is engaged therewith. That is, the main shaft 212 must be in a free state. This is useful when the reverse idler gear 262 and the sleeve gear 268 assume an out of phase relation, because the reverse idler gear 262 can be turned to match a gear tooth phase so as to engage the sleeve gear 268.
To this end, the interlocking plate 286 for preventing malfunction is usually formed with a cut-out portion 354. The cut-out portion 354 extends within a predetermined range of one surface of the interlocking plate 286. Movement of the second speed-synchronizing mechanism 272 is thereby limited to within the above predetermined range. When the cam mechanism 352 is struck by the cut-out portion 354, a spring 356 of the cam mechanism 352 is yielded and compressed, whereby the second speed-synchronizing mechanism 272 is released.
Further, a synchronizing device for a transmission is disclosed in, for example, Japanese Utility Model Application Examined No. 1-26894. The device disclosed in this publication employs a forward stage-synchronizing mechanism. At the time of reverse shifting, movement of a forward stage fork shaft is limited by a double engagement-preventing member, thereby allowing the forward stage fork shaft to be moved in such a limited path of movement. This arrangement reduces gear squeal during reverse shifting, and improves reverse operability as well.
In conventional types of reverse gear squeal-preventing structures, a second speed-synchronizing mechanism, i.e., a forward stage-synchronizing mechanism, is actuated and released via the resilient force of a spring. This arrangement produces a complicated relationship between spring strength, an operating force, and a synchronous effect. Consequently, it is difficult to decide a proper amount of the strength of the spring. In addition, when a speed change is rapidly performed, sufficient synchronization is impossible to achieve, and a gear squeal occurs. Further, an additional force is required for compressing the spring, thereby making operations heavier.
As a result, in order to transmit forces via the spring, it is necessary to use a spring sufficiently strong with respect to: actuation of the second speed-synchronizing mechanism; friction that occurs at portions of the second speed-synchronizing mechanism; and a positioning mechanism and the like. Furthermore, the operating force must be greater than is necessary in order to compress the spring at a final stage. This causes an inconvenience of reduced operability.
In order to obviate the above-described inconveniences, the present invention provides a reverse gear squeal-preventing device for a transmission having a main shaft, a counter shaft, and a reverse idler shaft arranged substantially parallel to each other within a transmission case, the main shaft being provided with forward stage main gears and a reverse main gear, the counter shaft being provided with forward stage counter gears and a reverse counter gear, and the reverse idler shaft being provided with a reverse idler gear, in which there is provided a shifting and selecting shaft adapted to provide axial movement at the time of selecting and providing pivotal movement at the time of shifting, depending on how a shift lever is controlled, and the shifting and selecting shaft is provided with an interlocking plate for preventing malfunction, whereby a forward stage-synchronizing mechanism is actuated at the time of reverse shifting so as to prevent gear squeal, the reverse gear squeal-preventing device characterized by a cam mounted on the shifting and selecting shaft so as to be only rotatable with respect to a pin that is inserted through the shifting and selecting shaft, a top portion of the cam being brought into and out of engagement with a forward stage-shifting yoke, and the shifting and selecting shaft being provided with a spring for pressing and urging the cam toward the interlocking plate.
Another aspect of the present invention provides a reverse gear squeal-preventing device for a transmission, as aforesaid, having a single cam movement-beveled surface provided at a side portion of the interlocking plate, a single beveled surface-engaging protrusion portion provided on a side surface of the cam for engaging the cam movement-beveled surface.
According to the present invention having the aforesaid structure, a shifting and selecting shaft has a pin inserted therethrough so as to allow a cam to be rotated in relation to the pin. In addition, a cam top portion is driven into and out of engagement with a forward stage-shifting yoke. Gears are thereby prevented from squealing during a shifting operation.
According to another aspect of the present invention having the aforesaid structure, a cam is rotated with respect to a pin which is inserted through a shifting and selecting shaft. A cam movement-beveled surface of an interlocking plate is engaged with a beveled surface-engaging protrusion portion of the cam, and a cam top portion is then disengaged from a forward stage-shifting yoke. Gears are thereby prevented from squealing during a shifting operation.